Many variations of sophisticated transducer positioning devices are known and used in the magnetic recording industry. A recent example of such a device which closely relates to the field of the present invention is described in U.S. Pat. No. 3,839,737. However, it has been found that a number of serious drawbacks regarding precise head-to-tape alignment, cost and complexity have been associated with the use of such devices.
These problems become particularly acute when processing video signals with linear tape transport devices, such as that disclosed in U.S. Pat. No. 3,921,933, in view of the high tape speeds involved. Due to physical and cost limitations on reel size, it is necessary to record a multiplicity of parallel program tracks across the width of the tape with such high-speed devices. The resulting shorter length of tape is passed repeatedly back and forth past the transducer head, information being recorded on or read from a different track with each pass of the tape.
With such a system operating at a tape speed of 120 inches per second, an 1800 foot reel of tape having twenty-eight parallel tracks can be used to record or playback a standard program of approximately ninty minutes duration. However, the requirement that twenty-eight different tracks be placed in parallel relation on a tape of reasonable width for consumer use has resulted in serious problems regarding alignment of the transducer head with the extremely narrow and closely spaced tracks on the tape. For example, recording twenty-eight tracks on a standard width 1/4 inch tape requires that the tracks be typically 6 mils in width with 2 mils spacing therebetween.
It has been found that prior methods of transducer positioning of reasonable cost and complexity were not sufficiently accurate or reproducible for use in such high-speed linear video systems intended for consumer use. Furthermore, these problems are compounded by the fact that the transducer must be moved almost instantaneously (i.e. in less than about 80 milliseconds) from one track to the next at the end of the tape as the system reversed in order to avoid visible interruption of the program material.
In addition, it is desirable that optimization of head-to-track alignment be easily and quickly obtainable by the user so as to provide for the interchangeability of tapes recorded on different machines without the necessity and expense of maintaining extremely high tolerance levels between machines.